square wave frequency representation

New to this signals stuff and i'm confused about the frequency representation of the square wave. Correct me if i'm wrong, a periodic square wave is composed of odd harmonics sine waves which are multiples of the fundamental frequency, In the frequency domain this just represents decreasing impulses at every odd multiple of the fundamental frequency . What relation does the sinc function have with the square wave? and which is the correct spectral representation of the square wave? Thanks!